As is known, knitting machines with latch needles are generally equipped with sinkers which cooperate with the needles in forming knitting.
More particularly, sinkers define a knitting forming plane on which the portion of knitting that lies between two contiguous needles rests while said needles, after engaging the thread at a feed or drop of the machine, retract into the needle holder in order to form a new loop of knitting and lower the previously formed loop of knitting and tension the loop of knitting on the shank of the needle while said needle is extracted with its tip and with part of its shank from the needle holder of the machine in order to engage the thread dispensed at a feed or drop of the machine and form a new loop of knitting. The engagement of the sinkers with the knitting which achieves tensioning of the loop of knitting on the shank of the needle, in this step, also prevents the loop of knitting from following the needle in its extraction movement and achieves assuredly the opening of the latch and the passage of the loop below said latch. The knitting loop tensioning action on the shank of the needle by the sinkers is generally assisted by traction of the already-formed knitted fabric, which is performed generally by means of pneumatic traction devices in small-diameter circular machines and by means of mechanical devices in the other machines.
Usually, the sinkers are located in appropriately provided slots which are formed, at the end of the needle holder from which the needles protrude to engage the thread at a feed or drop of the machine, directly in the needle holder or in a supporting element which is fixed to the needle holder. The sinkers are generally actuated by means of appropriately provided cams, which face the region of the needle holder in which the sinkers are accommodated and define paths which can be engaged by heels of the sinkers, which protrude from the needle holder, as a consequence of a movement of the needle holder with respect to such cams.
In many types of high-gauge knitting machine, in which the space between the needles is extremely reduced, there are no sinkers.
In these machines, the absence of the sinkers, forced by size requirements, causes problems and drawbacks. The absence of the sinkers, during accidental breakage of the yarn being knitted, in fact prevents automatic resumption of the formation of knitting and forces manual intervention to release the new loops of knitting on the shank of the needles which, as a consequence of the breakage of the thread, have lost the knitting.
Moreover, owing to the fact that in these machines the tensioning action of the loops of knitting on the shank of the needles while said needles are extracted with their tip from the needle holder to engage the thread at a feed or drop of the machine is performed exclusively by the fabric tensioning device, this tension can be insufficient, also due to the large number of needles which engage the knitting, to ensure the passage of the loops of knitting below the latch of the needles while said needles are extracted from the needle holder, causing knitting errors.
In order to limit these problems, in some cases these machines are actuated by moving to knit in each instance, at a feed or drop of the machine, only one needle of every two contiguous needles, so that the needle that is not used to form knitting performs a retention action on the loops of knitting formed by the contiguous needles which are made to knit. However, this solution has the drawback of not allowing to use fully the production potential of the machine.